This invention relates to a high-temperature secondary electrochemical cell and batteries of such cells that can be employed as power sources for electric automobiles, storage of energy generated during intervals of off-peak power consumption and various other applications.
A substantial amount of work has been done in the development of such electrochemical cells and their electrodes. The cells showing the most promise employ alkali metals, alkaline earth metals and alloys of these materials as negative electrodes opposed to positive electrodes including the chalcogens and metal chalcogenides as active materials. Typical examples include lithium, sodium or calcium and alloys of these active materials with more stable elements such as aluminum or boron as the negative electrode materials. In the positive electrode, active materials advantageously include metal sulfides or mixtures of transition metal sulfides such as the iron sulfide, cobalt sulfide, copper sulfide, nickel sulfide, cesium sulfide and molybdenum sulfide.
Examples of such secondary cells and their components are disclosed in U.S. Pat. No. 3,907,589 to Gay et al., entitled "Cathodes for a Secondary Electrochemical Cell" and in U.S. Pat. No. 3,947,291 issued Mar. 30, 1976 to Yao et al., entitled "Electrochemical Cell Assembled in Discharged State", U.S. Pat. No. 3,933,521 issued Jan. 20, 1976 to Vissers et al., entitled "Improved Anode for a Secondary High-Temperature Electrochemical Cell", U.S. Pat. No. 3,941,612 issued Mar. 2, 1976 to Steunenberg et al., entitled "Improved Cathode Composition for Electrochemical Cell", U.S. Pat. No. 3,933,520 issued Jan. 20, 1976 to Gay et al., entitled "Method of Preparing Electrodes with Porous Current Collector Structures and Solid Reactants for Secondary Electrochemical Cells", U.S. Pat. No. 4,006,034 issued Feb. 1, 1977 to Shimotake et al., entitled "Method of Preparing an Electrochemical Cell in Uncharged State", U.S. Pat. No. 4,011,373 issued Mar. 8, 1977 to Kaun et al., entitled "Uncharged Positive Electrode Composition", and U.S. Pat. No. 4,011,374 issued Mar. 8, 1977 to Kaun entitled "Porous Carbonaceous Electrode Structure and Method For Secondary Electrochemical Cell". Each of these patents is assigned to the assignee of the present application.
It has been previously been recognized that the addition of electrically conductive fillers incorporated into the positive electrode is advantageous. Electrically conductive metal powders of iron, cobalt, nickel, tungsten, molybdenum, niobium and powders of various other electrically conductive metals or carbon can be blended into the positive electroactive material. Usually, this electroactive material is formulated into a paste in which the transition metal chalcogenides as well as the selected halide and other additives are held together with a binder, the binder being either a suitable synthetic organic resin or a suitable electrolyte. One of the problems with the use of carbon as an electrically conductive filler or additive is that upon charge and discharge of the constructed cell, the carbon particles tend to agglomerate and to drift which reduces their electric conductive characteristics resulting in a degradation of cell performance.
Therefore, in view of these shortcomings in the prior art methods and cell produced thereby, it is an object of the present invention to provide a method of preparing an electrochemical cell with improved electrically conductive fillers therein and to provide an improved electrode structure produced thereby and to provide a new composition of matter.